Method of completing a well



April 30, 1968 E. cooK METHOD OF COMPLETING A WELL 2 Sheets-Sheet 1 Filed Dec. 21. 1965 FIG. 2

ATTORNEY April 30, 1968 L. cooK 3,380,532

METHOD OF COMPLETING A WELL I Filed Dec. 21, 1965 2 Sheets-Sheet 2 INVENTOR EVIN L. COOK (imam ATTORNEY United States Patent Q 3,380,532 METHOD OF COMPLETING A WELL Evin L. Cook, Dallas, Tern, assignor to Mobil Oil Corporation, a corporation of New York Filed Dec. 21, 1965, Ser. No. 515,464

16 Claims. (U. 166-46) ABSTRACT OF THE DISCLOSURE This specification discloses a process for completing a well into the earth whereby liquid drilling fluid employed during the drilling of the well does not enter the earth formation in which the well is completed, In the process, the well is drilled conventionally with liquid drilling fluid to a point in the vicinity of the top of the formation. Casing is then cemented in the well. Thereafter, a hollow liner which may be a closed end or open end liner is mechanically driven into the formation as by a pile driver, a hydraulic jar, or a vibration generator. Next, fluid communication is established between the interior of the liner and the formation.

This invention relates to the drilling of wells into the earth and relates more particularly to the completion of a well in an earth formation productive of a valuable fluid.

For the recovery of valuable fluids from earth formations, wells are drilled from the surface of the earth to the productive formations. In the drilling of these wells, a rotating bit is commonly employed and as the bit rotates and penetrates through the earth to the formation, earth material is dislodged in the form of cuttings. These cuttings are commonly removed from the well during the drilling operation by means of a drilling fluid. The drilling fluid is circulated downward through the drill pipe and upward through the annulus between the drill pipe and the wall of the well and carries the cuttings with it to the surface where they are removed from the fluid. While air or other gas may be employed as the drilling fluid, the use of gas is limited to particular situations. More commonly, a liquid, which may be water, oil, or an emulsion of oil and water in which the oil may be either the continuous or discontinuous phase, and which may contain solids such as clay and weighting agents, is employed. Various of the formations penetrated by the well, including the productive formation, contain fluids which are at pressures sufliciently high to flow from the formation to the well and such flow, when untimely, can seriously t interfere with operations. Where a liquid drilling fluid is employed, it provides an additional function of imposing a hydrostatic pressure on the formations penetrated by the well to prevent untimely flow of fluids from the formations to the well. For this reason, in addition to removing cuttings from the well, the drilling fluid is maintained in the well as a completion fluid when drilling through a productive formation where the pressure of the valuable fluid is sufficiently high to cause the fluid to flow into the well. The drilling fluid may also be maintained in the well when placing casing in a well penetrating such a formation and when carrying out other completion operations preparatory to putting the well on production.

Liquid drilling fluids are effective for the purposes intended. However, they often have a serious drawback due to their ability to invade, when sufficiently dense to overcome the pressure of the fluids in the formations penetrated by the well, porous earth formations including the productive formation. Frequently, the liquid constituting the liquid portion of the fluid has a damaging effect upon the productive formation. For example, aqueous drilling fluids can cause swelling of clays in a productive formation with the result that the permeability of the formation to the valuable fluid is seriously reduced. Consequently, the rate at which the valuable fluid may be produced from the formation to the well is greatly reduced. Similarly, other liquid drilling fluids can have other untoward effects in productive formations. Occasionally, corrective measures can be applied after the damage has been effected. However, it is ordinarily desirable to avoid such damage in the first instance. Further, additives may be employed in liquid drilling fluids to minimize invasion but such additives are not always entirely successful.

It is an object of this invention to avoid the damaging effects of liquid drilling fluids during the completion of a well.

It is another object of this invention to avoid reduction in permeability of a formation productive of a valuable fluid as a result of invasion of a liquid drilling fluid during the completion of the well.

These and other objects and advantages of the invention will become apparent from the following detailed description.

FIGURE 1 is a view, partially in cross section, schematically illustrating a well being drilled employing a rotating drill bit and a drilling fluid; I

FIGURE 2 is a view, in cross section, schematically illustrating the well of FIGURE 1 following drilling to the vicinity of the top of the productive formation, the cementing of the casing, and the drilling out of the cement p g;

FIGURE 3 is a view, in cross section, schematically illustrating the well of FIGURE 1 following mechanical driving of a hollow liner into the productive formation;

FIGURE 4 is a view, in cross section, schematically illustrating the well following removal of earth material from within the hollow liner;

FIGURE 5 is a view, in cross section, schematically illustrating the well following establishment of fluid communication between the interior of the liner and the productive formation; and

FIGURE 6 is a view, in cross section, schematically illustrating the method of well completion employing a closed end hollow liner provided with perforations.

In accordance with the invention, there is provided a method for completing a well drilled into an earth formation productive of a valuable fluid having a pressure sufliciently high to cause flow of fluid into the well which comprises as its essential steps mechanically driving a hollow liner into the productive formation from a point in the vicinity of the top of the formation and thereafter establishing fluid communication between the interior of the liner and the productive formation.

As stated, in the conventional method of completing a well, the well contains the drilling fluid as the drill bit penetrates the productive formation. Thus, in the conventional method, the drilling fluid, depending upon its den sity, is able to invade the productive formation during the completion operation. By the process of the invention, however, wherein a liner is driven mechanically into the productive formation from a point in the vicinity of the top of the formation, the liner penetrates the formation without any cuttings being produced which have to be removed from the well during the placement of the liner. Thus, a drilling fluid is not required. Moreover, even if the well in the vicinity of the top of the productive formation should contain drilling fluid, the drilling fluid cannot accompany the liner. Accordingly, by the method of the invention, drilling fluid is substantially kept from contact with the productive formation and invasion of the productive formation by the drilling fluid, and the consequent damaging effects, are minimized.

In the practice of the invention, the well is drilled initially by conventional methods employing a drilling fluid from the surface of the earth to a point in the vicinity of the top of the productive formation. Thus, the well may be drilled initially employing a rotary bit and conventional drilling fluids until the well has penetrated through the earth from the surface to a point in the vicinity of the top of the productive formation. This point may be just above the top of the productive formation. However, it may be at any greater distance above the top of the pro ductive formation but below the surface of the earth, In any case, the point is preferably sufliciently above the top of the productive formation that any liquid drilling fluid in the well at the time the liner is begun to be driven mechanically into the formation cannot gain access to the formation. Ordinarily, this distance need be no more than a few inches above the top of the productive formation. Although there is no restriction to penetrating partially the productive formation by the normal drilling process preceding the placement of the liner, some of the benefits resulting from this technique would be lost within that particular interval.

After the well is drilled to a point in the vicinity of the top of the productive formation by conventional methods employing a drilling fluid, casing is set in the well to the point where drilling is stopped. A single string, or several strings, of casings may be employed, depending upon requirements necessitated by the depth. to which the well was drilled. The final string, but preferably all of the strings where several are employed, is cemented. In the cementing procedure, the cement is pumped down through the interior of the casing and then upwardly within the annulus between the exterior of the casing and the wall of the well. The cement is then permitted to set in this position. As a result, a fluid-tight sheath surrounds the bottom of the well and isolates the well from fluid communication with any of the formations penetrated by the well.

Following cementing of the casing, the hollow liner is mechanically driven into the productive formation. In carrying out this procedure, any cement plug remaining at the bottom of the well first may be drilled out employing a conventional drill bit and a conventional drilling fluid. Alternatively, the liner can be mechanically driven through the cement plug and into the formation. However, where this latter procedure is employed, the bottom end of the liner driven through the cement plug may be severely damaged and the procedure is employed only where such damage, if any, is inconsequential,

The hollow liner to be driven mechanically into the productive formation may be of any suitable shape and constructed of any suitable material. The liner may be closed at one end, and the closed end terminated in a substantially sharpened point to facilitate penetration of the liner into the productive formation. However, a closed end liner requires a great deal of power to drive it mechanically into the productive formation. On the other hand, an open end liner requires less power to drive it mechanically into the productive formation and for this reason, an open end liner is preferred. Where an open end liner is employed, the liner, after being driven into the productive formation will be filled to the depth it was driven into the productive formation with a plug of earth material. A suitable liner is steel drill pipe or casing ordinarily employed in well operations. The liner may be provided beforehand with slots, or perforations of other shapes, to provide for subsequent fluid communication between the productive formation and the interior of the hollow liner. Where the liner is closed at one end and contains slots, or perforations of other shape provided beforehand, the liner is provided with a closure, such as a valve, in the vicinity of the upper end to provide a closed chamber within the hollow liner. With provision of the closed chamber within the hollow liner, premature flow of fluid from the producive formation into the hollow liner is substantially prevented since the fiuid pressure within the chamber will quickly become equal to that of the fluid within the formation. To establish fluid communication between the interior of the liner and the productive formation, the closure is opened.

For mechanically driving the liner into the productive formation, any technique suitable for this purpose may be employed. Thus, for example, a pile driver can be employed for driving the liner into the productive formation. This technique may be employed where the formation is not particularly thick, Also hydraulic jars used to loosen drill pipe and other equipment lodged in a wellbore may be used to drive the liner into place. Preferably, however, the liner is driven into the formation by a vibration generator suitably adapted to this purpose. The use of a vibration generator is particularly preferred where the formations to be penetrated are relatively thick. Any type of vibration generator may be employed provided that it is capable of inducing longitudinal vibration in the liner, preferably at a frequency which is characteristic of the material constituting the liner and the length of the liner. More particularly, the vibration generator preferably should be able to induce a longitudinal vibration having a frequency, or higher harmonics thereof, which is approximately equal to the quotient of the velocity of sound in the material of which the liner is constituted divided by twice the length of the liner. This isexpressed mathematically as:

wherein is the frequency of the vibrations of the liner,

1 is the length of the vibrating liner, and

c is the velocity of sound in the material consti ing the liner.

A particular type of vibration generator which may be employed in the practice of the invention is disclosed in Patent No. 2,975,846, issued Mar. 21, 1961 to A. G. Bodine, Jr. Another suitable vibration generator is the Bowen Hydraulic Jar, although the latter does not operate at some characteristic (resonant) frequency. The latter is disclosed in U.S. Patent No. 3,03 8,548.

In accordance with the other step of the invention, subsequent to the hollow liner being mechanically driven into the productive formation, fluid communication between the productive formation and the interior of the liner is established. The manner in which fluid communication between the productive formation and the interior of the hollow liner is established will depend upon the form of liner employed. Where a closed end liner is employed and the liner is provided with slots, or perforations of other shape, beforehand, fluid communication is established by removing the closure provided within the liner in the vicinity of its upper end. On the other hand, where an open end liner is employed, regardless of whether it is provided with slots or perforations of other shape, beforehand, establishment of fluid communication requires, at a minimum, removal of the plug of earth material accumulated within the liner. Removal of the plug of earth material can be effected by employing any of the conventional procedures for drilling within casing. Suitable procedures for removal of the plug of earth material are described in U.S. Patents Nos. 2,710,739 and 2,730,329, issued June 14, 1955 and Jan. 10, 1956, respectively, to A. P. J ourdain. Where the liner, whether having an open end or a closed end, has not been provided with perforations or other openings, fluid communication between the productive formation and the interior of the liner also involves a step of perforating the liner. For perforating the liner, any of the techniques heretofore employed for perforating casing in conventional completion practices may be employed. Thus, perforation may be effected by using bullets, jet perforators, or mechanical notching techniques. Where fracturing of the productive formation is employed following perforation or mechanical notching,

prevention of damage to the productive formation may be insured by employing a fracturing fluid which has no deleterious effect upon the formation.

A particular advantage of the invention resides in the absence of a cement sheath surrounding the casing at the productive formation. In conventional operations, the jet perforators, bullets, or fracturing techniques employed must not only provide fluid communication through the casing wall but also must provide fluid communication through the cement sheath. By the practice of the invention, there is no cement sheath surrounding the casing yet a fluid-tight connection is made between the casing and the walls of the penetrated formation. Thus, there is no cement to be penetrated and further there is no possibility of cement particles being driven into the formation at the perforations to reduce the permeability of the formations to the flow of the desired fluid.

The following will be illustrative of a procedure for carrying out the invention.

A well is drilled 3000 feet from the surface of the earth to a point just at the top of an earth formation, 200 feet thick, productive of petroleum. For this drilling, a rotary bit is employed. A conventional drilling fluid consisting of a suspension of clay in water, and containing barites to impart a sufliciently high density to the drilling fluid to provide a hydrostatic pressure sufficient to prevent flow of fluids from the drilled formations, including the productive formation, into the well, is employed. Following drilling to the 3000-foot level, casing is set in the well and the casing is cemented in place. For cementing, the cement is pumped through drill pipe displacing the drilling fluid upward through the annular space between the casing and the wall of the well. The cement follows the drilling fluid into the annular space and the cement is permitted to set within the annular space. Thereafter, the plug of cement at the bottom of the well is drilled out, the drilling fluid being employed to remove the cement cuttings and the drill pipe is removed from the well.

Following drilling out of the cement plug, a liner 200 feet long and consisting of sections of steel tubular casing, and open at the bottom end, is placed into the well, the drilling fluid remaining in the well. A vibration generator such as the type disclosed in the aforementioned Bodine Patent No. 2,975,846 is connected within the Well at the top of the liner. The liner being 200 feet long and the velocity of sound in steel being 16,000 feet per second, longitudinal vibration of the liner, in accordance with Formula 1 given hereinabove, is effected by actuating the vibration generator at about 40 cycles per second or higher harmonic thereof. With actuation of the vibration generator, the liner is allowed to penetrate into the productive formation and the hollow interior of the liner fills with a plug of earth material. The vibration generator is continued to be actuated until the line has penetrated for a distance of 190 feet into the productive formation and the top portion of the liner is then engaged (coupled) to the casing by means of a liner-to-casing adapter.

For effecting fluid communication between the interior of the liner and the productive formation, as a first step, the plug of earth material within the liner is removed by drilling, employing conventional drilling through casing technique. In this technique, a drilling fluid is used. There after, as a second step, the well is displaced free of drilling fluid with a suitable fluid to fill the hole during the final completion of the well. Next, as a third step, the liner is perforated over its entire length within the productive formation employing a gun perforator. With perforation of the liner, petroleum flows from the productive formation to the interior of the liner and it is brought to the surface of the earth through production tubing positioned within the liner.

Reference will now be made to the figures. Referring particularly to FIGURE 1, well is drilled from the surface of the earth 11 to a point near the top of productive formation 12. The well is provided with a surface liner 13 and the liner is cemented in place with cement sheath 14. Drilling of the well is effected by rotating drill bit 15 connected to drill pipe 20. Drilling fluid is pumped down through the drill pipe and the drilling fluid 21, after leaving the drill bit, flows upwardly through the well carrying the cuttings with it. The drilling fluid leaves the well through line 22 for separation of the cuttings and the fluid is returned to the well through the drill pipe 20. Drilling is continued in this manner until the well reaches a point just above the productive formation 12.

Following drilling to the point just above the productive formation, the drill bit and pipe are removed from the Well and, referring to FIGURE 2, an intermediate string of casing 23 is positioned in the well. This string of casing is cemented in place by means of cement sheath 24 and the plug of cement which remains within the well at the bottom of the casing following the cementing operation is drilled out leaving a space 25 below the casing providing access from the well to the earth 11. During the drilling of the plug of the cement, drilling fluid is employed to remove the cement cuttings from the well, and the drilling fluid is permitted to remain in the well following drilling out of the cement plug.

Referring now to FIGURE 3, following drilling out of the cement plug, hollow liner 29 is mechanically driven from the well 10 into the productive formation 12. The hollow liner 29 is an open end liner. This liner is mechanically driven into the productive formation by imposing longitudinal vibration to the liner by a pile driver, a hydraulic jar, or a vibration generator capable of inducing longitudinal vibration at a frequency characteristic of the material constituting the liner and the length of the liner. The longitudinal vibration may be induced in the liner at or above the surface of the earth, in which case the liner may be provided with a protective cap 30 during application of the longitudinal vibration. Alternatively, particularly where the productive formation 12 is at a great depth from the surface of the earth, the longitudinal vibration may be induced in the liner by a vibration generator positioned in the well at a point intermediate the surface of the earth and the productive formation 12. The hollow liner 29, upon application of the longitudinal vibration, is mechanically driven into the earth formation by displacement of the earth material and occupation by the liner of the space previously occupied by the earth material. A plug 31 of earth material fills the bottom of the hollow liner as the liner is driven into the productive formation.

The plug 31 of earth material is removed from the bottom of the hollow liner by drilling, using the drilling fluid 21 to remove the cuttings. The drilling fluid is removed from the well and is replaced with a suitable well completion fluid, as shown in FIGURE 4. The liner is now ready for establishment of fluid communication between the interior of the liner and the productive earth formation. As shown in FIGURE 5, communication is established by providing a plurality of perforations 33 in the liner employing a gun perforator, for example, for this purpose. Thereafter, the completion fluid may be removed from the well and the Well put on production.

FIGURE 6 illustrates another embodiment of the hollow liner. In this embodiment, a pointed end 34 closes the bottom of hollow liner 35. Further, the liner, before being positioned in the well, is provided with perforations 40. Moreover, the liner is provided at its upper end with a closure 41. The closure 41 is provided with a passageway 42 communicating with the interior of the liner and leading to line 43 provided with valve 44. The closure 41 also serves as a protective cap for application of longitudinal vibration and while the liner is being driven into the productive formation the valve 44 is closed. With the valve being closed, and the perforations being in contact with the earth material of the productive formation, the interior of the liner provides a closed chamber 45. This closed chamber prevents flow of fluid from the productive formation through the perforations 40 as the liner is driven into the formation. After the liner has been driven to the desired position in the productive formation, fluid communication is established by opening valve 44, thereby reducing pressure within the chamber 45 which permits fluid to flow from the formation into the liner.

Having thus described my invention, it will be understood that such description has been given by way of illustration and example and not by way of limitation, referonce for the latter purpose being bad to the appended claims.

I claim:

1. In a process of providing a well in an earth formation productive of a valuable fluid having a pressure sufficiently high to effect flow of said fluid from said formation into said well wherein said well is drilled from the surface of the earth to the vicinity of said earth formation employing during said drilling a rotating bit at the end of drill pipe to dislodge earth material in the form of cuttings and circulating a liquid drilling fluid within said well during said drilling to remove said out tings from said well and to impose a hydrostatic pressure on earth formations penetrated by said well to prevent flow of fluids from said formations to said well, the steps for completing said well and preventing invasion of said formation by said liquid drilling fluid during said completion comprising:

(a) discontinuing said drilling when said well has been drilled to a point in the vicinity of the top of said earth formation,

(b) removing said bit and said drill pipe from said well,

(c) driving mechanically a hollow liner from said well into said earth formation from said point in the vicinity of the top of said earth formation where said drilling of said well was discontinued, and

(d) establishing fluid communication between the interior of said hollow liner and said earth formation.

2. The process of claim 1 wherein said hollow liner is driven mechanically into said formation from a point above the top of said productive formation but below the surface of the earth.

3. The process of claim 1 where-in said hollow liner is an open end liner.

4. The process of claim 1 wherein said hollow liner is an open end liner and establishment of fluid communication between the interior of said hollow liner and said productive formation includes the step of removing earth material from the interior of said liner.

5. The process of claim 3 wherein said hollow liner is provided with perforations for subsequent fluid communication between said productive formation and the interior of said hollow liner.

6. The process of claim 4 wherein establishment of fluid communication between the interior of said hollow liner and said productive formation includes the additional step of perforating said hollow liner in place in said productive formation.

7. The process of claim 1 wherein said hollow liner is a closed end liner.

8. The process of claim 7 wherein establishment of fluid communication between the interior of said hollow liner and said productive formation includes the step of perforating said hollow liner in place in said format-ion.

9. The process of claim 7 wherein said hollow liner is provided with perforations for subsequent fluid communication between said productive formation and the interior of said hollow liner.

10. The process of claim 9 wherein said hollow liner is provided with a closure in the vicinity of the upper end thereof and establishment of fluid communication between the interior of said hollow liner and said productive formation includes opening said closure.

11. The process of claim 1 wherein said hollow liner is driven mechanically into said productive formation by applying longitudinal vibration to said hollow liner.

12. The process of claim 11 wherein said longitudinal vibration has a frequency or a higher harmonic thereof which is approximately equal to the quotient of the velocity of sound in the material of which said liner is constituted divided by twice the length of said liner.

13. The process of claim 1 wherein said hollow liner is driven mechanically into said productive formation by a pile driver.

14. The process of claim 1 wherein said well is drilled from the surface of the earth to the top of the productive earth formation employing a drilling fluid to remove cuttings from said well.

15. The process of claim 14 wherein said drilling fluid is a liquid drilling fluid.

16. A process for completing a well drilled from the surface of the earth to the vicinity of the top of an earth formation productive of a valuable fluid having a pressure sufficiently high to effect flow of said fluid from said formation to said well comprising driving mechanically a hollow liner into said formation from a point in the vicinity of the top of said productive formation but below the surface of the earth, said hollow liner being provided with a closure in the vicinity of the upper end thereof, and establishing fluid communication between the interior of said hollow liner and said productive formation by opening said closure.

References Cited UNITED STATES PATENTS 941,087 11/1909 Moore l6646 1,896,110 2/1933 Simmons 17557 1,908,217 5/1933 Blumenthal 175-19 1,944,481 1/1934 Wells l66208 3,049,185 8/1962 Herbold 17519 3,151,687- 10/1964 Sato et al. 175-95 3,187,513 6/1965 Guild 175--19 3,291,228 1 2/1966 Bodine 17555 3,314,478 4/1967 Burns l6649 JAMES A. LEPPI NK, Primary Examiner. 

